parent narrative

Newborn infants are ready to listen to sound and learn from it as soon as they enter the world. The sense of hearing is more developed than the sense of vision during early infancy and studies have shown that infants' early hearing skills are quite impressive. For example, newborns can distinguish between many of the different speech sounds they hear. They can also tell the difference between voices and different languages.

Despite these impressive abilities to distinguish between sounds, babies do not hear as well as adults. In fact, hearing takes a long time to fully develop. Researchers have shown that infants do not always encode sound precisely. What an infant hears during their first few months of life is likely a little "fuzzy" compared to what an adult hears.

The Onset of Auditory Function - Hearing Begins In Utero

Infants experience sound before they are born. The inner ear or cochlea starts to function in the second trimester of gestation. Audrey's mother may not know it, but Audrey has been listening to her voice in the womb! One remarkable consequence of this prenatal exposure to sound is that it can impact later speech perception. For example, within hours of birth most babies prefer to listen to the voice of their mother over the voice of an unfamiliar female saying the same thing.

Early Auditory Behavior - Responsiveness and Preferences

Babies are attracted to sound and will make responses to interesting or loud sounds in the first few months of their lives. Babies respond to sound in many different ways. For example, Nico's parents noticed that he would start or stop sucking when they spoke to him. Other infants will respond to sound by opening their eyes wide or grimacing. In response to loud sounds, most babies will startle. Researchers have named this startle in response to loud sounds a Moro reflex after the Austrian pediatrician who first noticed and described it.

Babies prefer to listen to some sounds more than others. For example, Audrey loves to listen to her parents' exaggerated voices when they talk to her. Researchers believe that the infant-directed speech or motherese adults use when they talk to babies makes it easier for them to hear and attend to voices.

Auditory Sensitivity - Rapid Improvements from Birth to Three Months

Young infants do not hear or respond to very quiet sounds like soft whispers or rustling leaves. Audiologists who assess hearing in the clinic and researchers who study hearing in the lab often measure the softest sound that a baby can hear at different frequencies or pitches. This measure is called an "auditory threshold". Auditory thresholds improve dramatically in the first few months of life. Three-month-olds can hear soft sounds that they could not hear just a few months before. This improvement in auditory sensitivity is thought to be caused by changes in a part of the ear called the middle ear. When the eardrum moves, three tiny bones in the middle ear vibrate and transmit the vibration to the inner ear. The shape and size of the middle ear changes during infancy. These changes allow the middle ear to transmit sound more efficiently.

Determining the Location of Sounds

Babies listen to sounds that are produced from many different locations in their environment. For example, Audrey loves to listen to her mother's voice when she is held in her arms. At other times, Audrey hears her parents talking several feet away while she is in her crib. It is amazing that even the youngest infants can localize sounds. In one study, researchers found that newborns will slowly orient to either the left or right toward a sound as long as their heads are properly supported.

Babies are not as good as adults at figuring out where sounds came from. One-month-old babies can only distinguish between sounds that are far apart. In comparison, adults can distinguish between sounds that are very close together.